what you don't understand anon is that Pearl can't decide anything when Rose is involved, Pearl will do whatever Rose wants even if this is not an order.
Pearl wanted to kill the baby Steven but she didn't do it cause she knew Rose loved that thing. Pearl didn't think what she was doing was wrong or though about the poor baby she knew was going to disappear but cause it wasn't what Rose wanted. Pearl is crazy because of her programming.
Pearl was still preaching how perfect and great Rose was even when she knew Rose did a lot of shitty choices, the way Pearl worships Rose shows her purpose as a Pearl is always speaking.